Children,
Cancer, and the Environment

Is Childhood Cancer
Increasing?

Whether childhood cancer
is becoming more common is a controversial question among scientists.

Data from the cancer tracking
systems in the US suggest that childhood cancer is increasing. The tracking
systems record new cases of cancer in some areas of the US. The largest tracking
system is called SEERand
is funded and overseen by agencies in the federal Department of Health and Human
Services.

The National Cancer Institute
and other agencies use the tracking information from SEER to try to determine
whether childhood cancer is increasing.

In 1996, the National Cancer
Institute reported that the frequency (incidence rate) for cancer of all types in children
increased 10% between 1973 and 1991. This means that 10% more new cases of cancers
per million children were found in 1991 than in 1973. During this period, brain
cancer and soft tissue sarcoma each increased more than 25%(1).

In 1999, the National Cancer
Institute reported that this increase in childhood cancer appeared to have leveled
off after 1990 (2).

One reason that it is difficult
to tell for sure whether rates are increasing is that changes are not consistent
from year to year. For example, the frequency of all childhood cancer cases
in 1995 was higher than 1994 for boys but lower than 1994 for girls.

To look at trends, it is
also important to look at differences for individual forms of cancer and not
just for the overall cancer rate.

NCI reported that, for
infants less than one year old, the cancer rate increased from 197.9
cases per million infants during the years 1976-84 to 264 cases per million
infants during the years 1986-94. This was a 36% increase (3). The greatest percentage
increase occurred for germ cell cancers (increase of 124%), central
nervous system cancers (increase of 57%), liver cancers (increase
of 50%), and neuroblastoma (increase of 35%).

In its monograph reporting
these increases, the National Cancer Institute comments that these increases
may be due to a variety of factors such as improved detection, rather than representing
true increases in cancer (3).

While the tracking system
are showing that more cases of childhood cancer were found in 1990 than in the
1970's, different people interpret this reported increase in different ways.
Some people believe that the reported increase in the number of cases reported
do not represent real increase in disease.

There are several reasons
why the number of new cases of a disease may go up.

One, of course, is that
the disease may become more common. This would be a "real" increase
in disease.

However, the number of
cases of a disease could also go up if people's access to medical care increased,
so that more people got tested for the disease, and more cases were found.

A third reason that number
of cases reported could go up is if better methods or technologies are adopted
so that cases are found that would have otherwise not have been detected.

A fourth reason is that
sometimes the way that doctors define disease changes, so that more types of
tumors may be counted as cancer, for example.

Scientists disagree about
which of these reasons apply to the increase in cancer in children.

Many scientists believe
that the increases reported reflect a real increase in disease. Dr. Phil Landrigan
of the Mt. Sinai Hospital of New York says that almost all cases of brain cancer
are found, so the changes in technology cannot be the reason that the disease
is found more often (4).

Other scientists disagree.
For example, scientists from the National Cancer Institute have argued that
all of the increases in brain cancer in children are because new methods are
better at detecting the cancer than those used in earlier years (5,
6).

The Good News: Mortality
is Decreasing

Another way to measure
changes in cancer is to look at the mortality (or death) rate. This counts the
number of people in a group that die from a disease over a defined period, usually
a year. Mortality rates are generally influenced by the effectiveness of medical
treatments. If many people get a disease but the treatment is very effective,
only a few will die. In this example, the mortality rate will be low even though
the incidence rate is high.

One area of very good news
related to childhood cancer is that treatments for many cancers have improved
greatly over the last few years. As a result, mortality rates are generally
going down.

From a statistical point
of view, this means that mortality rates are not a good way to keep track of
how common childhood cancers are.